Left panel: curved slit used for the LUCI-ARGOS observations on a HST infrared image of the 8 o’clock arc covering the three multiple lensed images of the galaxy at z = 2.73. Right panel: 2D spectra of all lines observed in the H and K bands at 55 km s⁻¹ spectral resolution. The integration times and spatial resolution of each band are t_int(K)=2 h, PSF(K)=0.35^′′ and t_int(H)=3.9 h, PSF(H)=0.35^′′.